Dredging

the deepening of channels and harbors by the removal of loose earth. There are two typical kinds of dredging machines. The first consists essentially of a series of buckets, running on an endless chain or belt, such as may be seen in a grain elevator, only on a larger scale. As the buckets pass around the lower pulley, they scoop up earth; as they run over an elevated pulley at the other end of the circuit, they discharge the earth into a scow provided for the purpose of receiving it. Huge dredges of this sort are in use in digging the Panama Canal.

A second sort of dredge consists of a steam shovel, such as is used for loading earth on flat cars. The shovel, which is really a huge, metal scoop, has the size of a barrel. It is swung on a derrick and is worked by steam. It drops to the bottom and scrapes up a load of earth. It is then elevated by means of a chain and ratchet work, and swung around by means of the derrick until in position to discharge its contents through a hinged bottom into a scow as before. Both kinds of dredge are mounted on a flat boat constructed for the purpose. It carries an engine and a supply of fuel. It advances as the work progresses and may be taken from place to place as its services are needed. Still another kind of dredge may be mentioned. A colossal contrivance, used in deepening the channel of the Willamette and Columbia rivers, churns up the soil to be removed and pumps it up like a mosquito, through a forty-inch tube. Mammoth dredges are kept at work constantly in the Suez and other canals.